Like he said bro. Checking the run off pH is highly overrated, and its not an accurate representation of the coco medium. To get a better pH value of the coco do a slurry test. But the only time I check my Coco's pH is when I'm having savage defiencies, which is rare.how i do it...
1). fill jug with filtered water
2). add nutes
3). ph water accordingly 5.5-6.0
4). feed plants.
checking runoff doesn't really do jack...and i killed a plant think just like that.
if you have only a few plants and mix your nutes per gallon ~like me~ then you will want to check the ph before every feeding.